Can a sub-$100 graphics card get the job done?

...and just how much should you spend on graphics, anyhow?by Scott Wasson  8:44 PM on September 24, 2008

We have not, I must admit, been great fans of sub-$100 graphics cards here at TR. Yes, we've reviewed them pretty faithfully over the years, but as I said in our review of the Radeon HD 2400 series: "If you're spending less than [$100] on graphics, you're getting the sort of performance you deserve, regardless of which brand of GPU you pick." In other words, cheaping out will get you lousy frame rates and spotty gameplay. It wasn't just spite to say so; it was definitely true.

But what if you could cheap out and get more than you deserve for it? What if, through the magic of technological progress, dropping 80 bucks on a video card could get you a GPU that will slice through the latest games with relative ease? What if it could help decode HD video streams perfectly, even on a slow CPU? If such a beast existed, should you consider spending more, or would it just be future-proofing and fluff?

Exhibit A in our quest for knowledge is the brand-spanking-new Radeon HD 4670 graphics card, which threatens to tilt our assessment of the market on its ear. The 4670 inherits its GPU DNA from the Radeon HD 4800 series, which crams a tremendous amount of graphics power into a relatively small chip. AMD has scaled down this same basic design to fit into a budget-class GPU, and in doing so, it has brought unprecedented levels of graphics power to spendthrifts everywhere. To put the 4670's graphics power into perspective, this $79 card has twice the shader power and three times the texturing capacity of the most capable game console, the Xbox 360 (assuming the spotty info on game consoles I found out there is correct.) If you're more of a PC-oriented person, consider this: the 4670 has roughly equivalent shader power and over twice the texturing capacity of the Radeon HD 2900 XT, the first DirectX 10-class Radeon, a high-end card which debuted at under $400 18 months ago. And the 4670's architecture is arguably more efficient.

There are mitigating factors here, of course. The biggest one is the 4670's relatively anemic memory bandwidth, which is under a third of the 2900 XT's. But the trends are favorable for cheapskates, for a variety of reasons. Better compression, smarter caching, and the proliferation of programmable shaders may mean memory bandwidth is at less of a premium, for instance. Not only that, but AMD's competition over at Nvidia has responded to the 4670 by adding another cheap video card to its portfolio, as well. The affordable entries in these two firms' product portfolios stretch from about 60 bucks to 170 bucks, with multiple increments in between. Even if the dirtiest of dirt-cheap video cards won't cut the mustard, surely something in there will. The questions is: How little can you get away with spending? Let's take a look.

The Radeon HD 4670 steps up
The Radeon HD 4670 doesn't look like much at first glance. In fact, it looks like pretty much any other low-end graphics card.

However, fitting that profile isn't a bad thing at all, really. A card like this one will easily go into just about any PC, maybe even that cheapo HP that you picked up at Costco without realizing its built-in graphics sucked harder than a Dyson. The board itself is just over 6.5" inches long, and it's content to draw power solely from the PCI Express slotno auxiliary power connection needed. AMD rates the 4670's peak power draw rather vaguely at "under 75W," the max a PCIe slot can supply, but still not terribly much. Even most cheap power supplies should be able to keep this puppy fed.

Lurking beneath that modest cooler is an RV730 GPU. If you'll permit me to geek out a little bit, I'll give you its specs. Like its big brother RV770, the RV730 is a DirectX 10.1-capable graphics processor with a unified shader architecture and a full suite of modern features. The RV730 chip is quite a bit smaller than its older sibling, though. Manufactured by TSMC on a 55nm process node, the RV730 has an estimated 514 million transistors stuffed into an area of 145 mm². In the RV730, AMD has cut down the RV770 design by halving the number of shader execution units per SIMD partition from 16 to eight and by reducing the number of SIMD partitions from 10 to eight. What's left are 64 superscalar execution units, each of which has five ALUs. Multiply that out, and you have 320 ALUs or stream processors (SPs), as AMD likes to call them.

As I've said, that's quite a bit of shader power, with just as many SPs as the Radeon HD 2900 XT, though the RV730's SPs should be more efficient and have a few new capabilities, including DirectX 10.1 support. AMD has made one concession to the RV730's budget status by removing native hardware support for double-precision floating-point math, a feature really only used by non-graphics applications tapping into AMD's stream computing initiative. The rest of the compute and data sharing provisions built into the RV770 remain intact in the RV730, though.

The outlook gets even rosier for the Radeon HD 4670 when we consider texturing capacity, a weakness for prior Radeons but a strength here. Because this architecture aligns texture units with SIMD partitions, the RV730 has eight texture units, each of which is capable of sampling and filtering four texels per clock. That's 32 texels per clock from a low-end GPU, not far at all from the 40 texels/clock of the Radeon HD 4850 and 4870.

The RV730 has only two render back-ends, each of which can write four pixels per clock to the frame buffer. Yet those render back-ends are quite a bit more capable than the ones in the Radeon HD 2000 and 3000 series, with twice the throughput for multisampled antialiasing, 64-bit color formats, and depth/stencil only rendering. In practical terms, the RV730 should be even more capable, relatively speaking, since the render back-ends in those older Radeon HD 2000- and 3000-series GPUs had to rely on shaders to help with some of the antialiasing work. The RV730 does not. The two render back-ends each sit next to a 64-bit memory controller, giving the RV730 an aggregate 128-bit path to memory. That's half what you'll get in a $149 video card, but twice what you might expect from a $79 one.

Wow, so I really geeked out there. Sorry about that.

Back on planet Earth, the Radeon HD 4670 will come in two versions. Both will have a 750MHz GPU and shader core, but they'll differ in memory size and speed. The first version will have 512MB of GDDR3 memory clocked at 1GHz, for an effective 2GT/s. This is the version we have in Damage Labs for testing, and it's probably the more sensible of the two. The second will have a full gigabyte of GDDR3 memory at a lower 900MHz clock and 1.8GT/s data rate. Either one should set you back just a penny shy of 80 bucks, according to AMD, and indeed, there's a 512MB MSI card selling for exactly that price at Newegg right now.

(I guess, technically, I should say it's a "512 MiB" card, but I'd rather claw my eye out with a fork.)

The cards come with a couple of dual-link DVI outputs and a TV-out port. Our sample came with a dongle to convert the TV-out port to component video and another to convert a DVI port to HDMI.